High power light absorbers having anti-reflection coating

Abstract

High-power light absorbers (HPLAs) can exhibit low back-scattered light, mitigate stray light, and withstand high optical power. The absorbers can be used with or without baffling as beam dumps for high-power lasers. An HPLA may include a substrate made of high thermally conductive material with an anti-reflection (AR) coating formed on the substrate. A thin layer of highly absorbing material may be located between the AR coating and substrate. The substrate can be cooled with a fluid, such as water or air.

The invention claimed is: 
     
       1. A light absorber for absorbing incident light, the light absorber comprising:
 an anti-reflection coating to pass transmitted light that is a portion of the incident light; 
 a first absorbing layer comprising a metal or a semiconductor to absorb a portion of the transmitted light; and 
 a thermally conductive substrate, in thermal communication with the first absorbing layer, to dissipate heat generated by absorption of the portion of the transmitted light by the first absorbing layer, such that the light absorber has a damage threshold of at least 100 watts per square centimeter (W/cm 2 ) and wherein the light absorber reflects less than 1% of the incident light. 
 
     
     
       2. The light absorber of  claim 1 , wherein the thermally conductive substrate comprises at least one of a metal, a semiconductor, or a glass. 
     
     
       3. The light absorber of  claim 1 , wherein the anti-reflection coating comprises at least two layers of silicon oxide, titanium oxide, tantalum oxide, or hafnium oxide. 
     
     
       4. The light absorber of  claim 1 , wherein a thickness of any one layer in the anti-reflection coating is no greater than 250 nm. 
     
     
       5. The light absorber of  claim 1 , adapted to absorb at least 70% of the incident light having a wavelength between 300 nm and 1500 nm and a power density of at least 100 W/cm 2  and reflect no greater than 0.05% of the power of the incident light. 
     
     
       6. The light absorber of  claim 1 , further comprising a second absorbing layer located within the anti-reflection coating. 
     
     
       7. The light absorber of  claim 1 , further comprising a conduit, running through the thermally conductive substrate, to convey a cooling fluid through the thermally conductive substrate. 
     
     
       8. The light absorber of  claim 7 , adapted to receive up to 100 kW of optical power without damaging the light absorber. 
     
     
       9. The light absorber of  claim 1 , further comprising at least one dielectric layer disposed between the first absorbing layer and the thermally conductive substrate. 
     
     
       10. The light absorber of  claim 9 , wherein the first absorbing layer, the at least one dielectric layer, and the thermally conductive substrate form a Fabry-Perot resonator. 
     
     
       11. The light absorber of  claim 1 , combined with a reflective beam dump, in optical communication with the light absorber, to multiply reflect a beam of light propagating in a first direction and produce, at least in part, the incident light, wherein the reflective beam dump includes a second absorbing layer and is configured to absorb a fraction of power of the beam of light for each reflection of the beam of light from the reflective beam dump. 
     
     
       12. The light absorber of  claim 11 , wherein the reflective beam dump has a specular surface to provide the multiple reflections. 
     
     
       13. The light absorber of  claim 1 , wherein the first absorbing layer is a single layer of the metal or the semiconductor. 
     
     
       14. The light absorber of  claim 13 , wherein the first absorbing layer has a thickness between 10 nanometers and 2 microns and is disposed directly on the thermally conductive substrate. 
     
     
       15. The light absorber of  claim 13 , wherein the first absorbing layer has an optical extinction coefficient greater than that of the thermally conductive substrate. 
     
     
       16. The light absorber of  claim 13 , wherein a surface of the first absorbing layer is roughened to diffuse the transmitted light. 
     
     
       17. The light absorber of  claim 13 , wherein the first absorbing layer is formed from tungsten, the substrate is formed from copper, and the anti-reflection coating comprises two layers of silicon oxide and two layers of titanium oxide. 
     
     
       18. The light absorber of  claim 17 , wherein:
 the first absorbing layer is between 90 nm and 110 nm thick; 
 a first titanium oxide layer of the two layers of titanium oxide deposited on the first absorbing layer is between 80 nm and 100 nm thick; 
 a first silicon oxide layer of the two layers of silicon oxide deposited on the first titanium oxide layer is between 180 nm and 200 nm thick; 
 a second titanium oxide layer of the two layers of titanium oxide deposited on the first silicon oxide layer is between 80 nm and 100 nm thick; and 
 a second silicon oxide layer of the two layers of silicon oxide deposited on the second titanium oxide layer is between 95 nm and 115 nm thick. 
 
     
     
       19. A method of absorbing incident light with a beam dump having a thermally conductive substrate made of a first material, the method comprising:
 absorbing a first portion of the incident light with an absorbing layer made of a second material that is different from the first material and is deposited on or over a surface of the thermally conductive substrate, wherein the incident light has an intensity of at least 100 watts per square centimeter (W/cm 2 ); 
 conveying heat from the absorbing layer to the thermally conductive substrate; 
 dissipating heat from the thermally conductive substrate; and 
 reducing reflection of the incident light from the absorbing layer and the thermally conductive substrate with an anti-reflection coating such that the beam dump reflects less than 1% of the incident light. 
 
     
     
       20. The method of  claim 19 , further comprising reflecting the incident light one or more times from a reflective beam dump before absorbing the first portion of incident light. 
     
     
       21. The method of  claim 19 , further comprising specularly reflecting a second portion of the incident light from the beam dump. 
     
     
       22. The method of  claim 19 , further comprising diffusing reflected incident light from the beam dump with a roughened surface of the absorbing layer. 
     
     
       23. The method of  claim 19 , wherein the surface of the thermally conductive substrate is roughened to have a peak-to-peak roughness equal to or greater than 500 nm over a 1 cm 2  area. 
     
     
       24. The method of  claim 19 , wherein a dielectric layer is located between the absorbing layer and the thermally conductive substrate. 
     
     
       25. The method of  claim 24 , further comprising resonating the incident light between the thermally conductive substrate and the absorbing layer in a Fabry-Perot resonator formed, at least in part, by the thermally conductive substrate, the dielectric layer, and the absorbing layer. 
     
     
       26. An absorbing beam dump comprising:
 a thermally conductive substrate formed from a metal or semiconductor to repeatedly receive, without being damaged, incident light having an intensity of at least 100 watts per square centimeter (W/cm 2 ) and allow the incident light to propagate into the thermally conductive substrate a distance greater than one wavelength of the incident light and be absorbed by the thermally conductive substrate; and 
 a multi-layer antireflection coating formed on the thermally conductive substrate to suppress reflection of the incident light from the thermally conductive substrate such that the absorbing beam dump reflects less than 1% of the incident light. 
 
     
     
       27. The absorbing beam dump of  claim 26 , further comprising a structure formed on or around the thermally conductive substrate to allow a gas or a liquid to flow and contact the thermally conductive substrate so as to remove heat from the thermally conductive substrate.